How to Safely Erase Map Elements While Iterating in C ?

Potential Pitfalls When Erasing Map Elements During Iteration

When manipulating maps in C , it's crucial to consider the consequences of erasing elements while iterating through them. This question explores the potential issues and provides solutions for both C 03 and C 11.

C 03 Considerations

In C 03, erasing an element from a map does not automatically invalidate all iterators in the map. However, it does invalidate the iterator pointing to the deleted element. To safely iterate through a map and erase elements during iteration, you need to increment the iterator before calling erase. Here's an updated version of the code provided in the question:

map<string, SerialdMsg::SerialFunction_t><string, SerialdMsg::SerialFunction_t>::iterator pm_it = port_map.begin();
while (pm_it != port_map.end()) {
    if (pm_it->second == delete_this_id) {
        port_map.erase(pm_it++);  // Use post-increment to get the updated iterator.
    } else {
        ++pm_it;  // Can use pre-increment for efficiency.
    }
}

C 11 Enhancements

In C 11, the erase() method has been significantly improved. It now returns an iterator pointing to the next element in the map, making it safe to erase elements during iteration without invalidating other iterators. The updated code using C 11 would be:

auto pm_it = port_map.begin();
while (pm_it != port_map.end()) {
    if (pm_it->second == delete_this_id) {
        pm_it = port_map.erase(pm_it);
    } else {
        ++pm_it;
    }
}

Mark Ransom Technique

The Mark Ransom Technique is another option in C 03 for safely erasing map elements during iteration. It involves creating a temporary vector to store the keys of the elements to be erased and then erasing them in a second loop.

In conclusion, when erasing elements from a map during iteration in C , take into account the potential invalidation of iterators and use the appropriate approach depending on the C version you are using. Remember to always increment the iterator before erasing an element to maintain consistency and avoid unexpected behavior.

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